Digital media have been widely used. Some automobiles use recorded multi-channel music sources for reproduction in the passenger room. The present invention relates to a car-borne sound system for reproducing multi-channel music sources in high quality sound.
Taking advantage of recent digital recording media of high recording capacity, for example a DVD Audio, it has become popular to record music in multi-channel way with an aim for improving the feeling of presence at audience. The multi-channel systems in practical use include; the 5-channel system where the recorded channels are reproduced respectively by the speakers disposed at the front right, the front, the front left, the rear right and the rear left of a listener. A so-called 5. 1 channel system, which is provided with a sub-channel recording only low frequency range sound components, has also been made available.
In the home-use sector, a sound system that offers sounds with a superior feeling of presence by reproducing sound signals through speakers disposed at a front right, a front center, a front left, a rear right and a rear left of audience plus a speaker exclusive for low frequency range sound reproduction has already been developed and in practical use. On the other hand, development activities regarding a car-borne sound system for reproducing the multi-channel music sources in a room of an automobile with a superior feeling of presence have just started.
FIG. 10 shows a conventional sound system for reproducing the recorded multi-channel sound sources in a room of an automobile, based on the above-described 5. 1 channel system. A reproduction apparatus 1001 reproduces a 5. 1 channel music source into electric signals; a front right signal and a front left signal are supplied respectively to a front right speaker 1003 and a front left speaker 1004, while a rear right signal and a rear left signal are supplied respectively to a speaker 1005 disposed in the rear right door and a speaker 1006 disposed in the rear left door. As to a front center signal, in some cases it is supplied for reproduction to a speaker 1002 disposed in the center of a dashboard. However, it is often very difficult to provide a speaker in the center of a dashboard. In such a case, the front center signal is added on to the front right and the front left signals, as an exemplary compensation, so that the speakers 1003 and 1004 disposed in the front right door and the front left door reproduce also the front center signal components.
When placing speakers in an automobile, the front speakers are normally disposed in the front right door and the front left door and the rear speakers in the rear right door and the rear left door (or, at the right and the left of a rear tray). Under the above speaker layout, a conventional stereo signal reproduction system supplies the right-channel signal to the speakers disposed in the front right door and the rear right door (or, at the right of tray), and the left-channel signal to the speakers in the front left door and the rear left door (or, at the left of tray), for reproduction of sound. It is obvious that the basic role for the speakers disposed in the rear doors or the tray is to provide passengers sitting in the rear seat with sounds for their listening. At the same time, the rear speakers bear an important function of improving the sound quality and the sound image perceived by those who are sitting in the driver""s seat and the front seat.
The reason: in the normal case where the speakers are mounted only in the front right door and the front left door and a stereo signal is reproduced therefrom, listening point in the front seat is either at the driver""s seat or the front passenger seat, which is substantially off the center between the right and the left speakers. The listening point in this case is deviating greatly to the right, or to the left. Under such condition, much time lag and much difference in the sound pressure are perceived at a listening point between the sound waves reaching from the right and the left speakers; as the result, the sound image is positioned at a point which is very close to a speaker adjacent to the listening point.
This phenomenon of sound image deviation is significant with the monaural signal components contained among the right and the left signals of a stereo source. A human vocal sound, which is consisting mainly of monaural components and should naturally be located in the middle of the right and the left speakers, is positioned at a location adjacent to either one of the right and the left speakers. This causes an unnatural feeling with a listener.
When the same stereo signals as above are reproduced also from the speakers in the rear doors, or in the rear tray, the sound fields are moderately stirred and the difference in the time of arrival and the sound pressure at a listening point (driver""s seat or front passenger seat) between the right and the left sound waves is eased, as compared with the case when sounds are reproduced only from the speakers in the front right door and the front left door. The human vocal sound (human singing sound) which contains much monaural components is not heard deviated to either one of the speakers. It sounds naturally, with the sound image fixed in a central zone.
As described above, it is of a substantial importance, in the making of natural vocal sound in a car room, to additionally provide the rear right speaker and the rear left speaker disposed in the rear doors, or in the rear tray, with the same signals as those supplied to the speakers of the front right door and the front left door, or adding an influential monaural signal component.
In the multi-channel sound recording system (5. 1 channel system), vocal components are recorded mainly in the front center signal and the right and the left front signals. When the music source is reproduced in an automobile room using a conventional system as shown in FIG. 10, the vocal components are reproduced only from the speakers in the front right door and the front left door. Then, as s described earlier regarding the logic of stereophonic sound reproduction in a car room, the time lag and the difference in sound pressure at a listening point between the sound waves arriving from the speakers remain significant, and the vocal sound image is positioned unnaturally deviating to a place adjacent to either one of the speakers.
The present invention addresses the above-described drawbacks, and aims to provide a car-borne sound system that can reproduce a music source with the vocal sounds at a natural positioning.
A car-borne sound system of the present invention comprises:
a 5-channel music source recorded for reproduction through the speakers disposed in the front center, in the front right, in the front left, in the rear right and the rear left of a listener, or a 4-channel music source recorded for reproduction through the speakers disposed in the front right, in the front left, in the rear right and the rear left of a listener;
a reproduction apparatus for reproducing the music source into electric signals;
a signal processing apparatus for processing the multi-channel signals supplied from the reproduction apparatus; and
a plurality of speakers disposed within a room of an automobile for radiating sound outputs based on the multi-channel electric signals delivered from the signal processing apparatus.
In the car-borne sound system of the present invention, the signal processing apparatus delivers an output signal for the rear right after adding a part of the front signals such as the front center signal, the front right signal and the front left signal, which contain much of the vocal components, on the rear right signal supplied from the reproduction apparatus. And it delivers an output signal for the rear left after adding a part of the front signals such as the front center signal, the front right signal and the front left signal on the rear left signal supplied from the reproduction apparatus. In this way, car-borne sound systems of the present invention reproduces high quality sound environment rich in the feeling of presence in a car room taking advantage of the multi-channel sound source, without causing the unnatural positioning of vocal sound image which was considered unavoidable with conventional car-borne sound systems.